1. Field of the Invention
The present invention relates to a current driving circuit for outputting a plurality of output currents corresponding to a reference current.
2. Description of the Prior Art
As loads which need to be operated by constant-current, a LED (light emitting diode) display panel in which a plurality of light emitting diodes are arranged, an organic EL (electro luminescence) display panel in which a plurality of organic EL devices utilizing the electroluminescence phenomenon of an organic compound are arranged, and the like have been known. In such a display panel, a plurality of LEDs or organic ELs are used as light emitting devices and the display panel has a large display area. Therefore, a current driving apparatus for driving a display panel can not be formed of a single current driving circuit (IC). For this reason, in general, a plurality of current driving circuits are used for a single display panel so that driving operation is shared and performed by the plurality of current driving circuits.
FIG. 13 is a block diagram illustrating an exemplary known current driving circuit. The current driving circuit includes two current driving circuits 90 and a reference current supply circuit 91. Each of the current driving circuits 90 includes a reference current input terminal 901, a bias voltage generation transistor 902, n (n is a natural number) driving transistors 903-1 through 903-n and n output current output terminals 904-1 through 904-n. Each of the current driving circuit 90 outputs n output currents Iout-1 through Iout-n each having a current value corresponding to a given reference current Iref. The reference current supply circuit 91 includes PMOS transistors 911, 912-1 and 912-2. The reference current supply circuit 91 supplies the reference current Iref to each of the current driving circuits 90. In FIG. 13, the number of current supply circuits 90 is 2, the reference current supply circuit 91 is formed so as to supply two reference currents.
However, in a conventional technique, only a predetermined number of current driving circuits can be used. Specifically, because a reference current has to be supplied to each current driving circuit, the number of current driving circuits can not be larger than the number of reference currents to be supplied. As described above, the number of current driving circuits to be used is limited depending on a structure of the reference current supply circuit, so that the number of current driving circuits to be used can not be freely changed.